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914World.com _ 914World Garage _ Valve Clearance?
Posted by: last337 Aug 19 2013, 02:33 PM
Can someone explain this to me? I have been fighting with this thing for some time now. I had so many problems for so long with my engine just dying and after pulling my tank and changing fuel lines and filters I am back running again.
Now I am having another issue where I will get my dual carbs tuned just right at operating temp and be running just fine. However, after a while I start to hear backfiring again. The only thing I havent done in a while is set my valve clearances. Actually it has been a long while since I have done that and I am suspicious about it being the culprit.
I understand how if my timing was off or my mixture was off I could hear pinging or backfiring through the exhaust. But I dont know why my valve clearance would do that only as the temp of the engine changes or just seemingly by itself at times.
Can someone explain how proper valve clearance is so critical?
Posted by: r_towle Aug 19 2013, 02:42 PM
Valves set to tight will remain open longer than they are supposed to.
Creates hard starting, low power, and backfires up the intake.
Valves too loose creates lots of valve tappit noise and lower power due to not opening enough.
Valves are set cold because as the engine warms up, the aluminum push rods get longer...so you end up with zero lash when hot.
Setting them hot sucks, but can be done....wear gloves.
If your carbs are getting worse as the motor gets hotter, you need to be looking at possibly intake leaks, and possibly linkage binding up when hot.
Here is how I put gaskets on the carb setup to prevent boiling the fuel when the motor gets hot.
Another "car runs worse when hot" issue.
It also prevents intake leaks.
head
rtv sealant
gasket
phenolic spacer
gasket
rtv sealant
manifold
then
rtv sealant
gasket
spacer (sometimes, not always...unless I have having boiling issues)
gasket
rtv sealant
Now, I use the sealant very very thin.
Its just smeared on both sides of the gasket to ensure a tight seal to the head and the spacer.
I have found that most of my leaks are head to manifold and not manifold to carbs...but that is my experience.
Sometimes I have needed to trim the gasket and the spacer to get around and away from the cylinder head tin which can intrude on me trying to get a tight seal down there...
One more issue when hot.
Distributor advance plates with OEM grease from 40 years ago stop moving.
The grease is more like glue now...
Fix is to remove advance plates, take them apart, clean and re-grease.
Put it all back in place...
Its another super hot thing when the motor is running...cant touch the distributor.
RIch
Posted by: last337 Aug 19 2013, 03:29 PM
Thanks for the info! I guess I need to go through it again then.
Do you know where I can buy the phenolic spacers? I cant seem to find a vendor for anything other than the paper gaskets.
Posted by: last337 Aug 19 2013, 04:05 PM
I see a few on ebay but would rather get them somewhere else.
Posted by: monkeyboy Aug 19 2013, 04:50 PM
HAM sells them
Posted by: last337 Aug 19 2013, 05:08 PM
HAM sells them
HAM?
Posted by: euro911 Aug 19 2013, 05:25 PM
Do you know where I can buy the phenolic spacers? I cant seem to find a vendor for anything other than the paper gaskets.
There's a guy on the board (Carl), who goes by MRRAGPICKER that sells 1.7L and 1.8L spacers pretty cheap
Posted by: jsayre914 Aug 19 2013, 05:27 PM
HAM sells them
HAM?
http://www.hamincgroup.com/vw.php
Posted by: Dave_Darling Aug 19 2013, 05:29 PM
http://haminc.biz -- Len Hoffman, Hoffman Automotive Machining. Knows more about Type IV cylinder heads than probably anyone alive.
The standard "gaskets" used in fuel-injected applications are phenolic block spacers. So all of your favorite Porsche or 914 specialists will carry them as well. (My favorite is in my sig, but I'm a bit prejudiced.)
--DD
Posted by: last337 Aug 19 2013, 05:31 PM
Do you know where I can buy the phenolic spacers? I cant seem to find a vendor for anything other than the paper gaskets.
There's a guy on the board (Carl), who goes by MRRAGPICKER that sells 1.7L and 1.8L spacers pretty cheap
I have a 2.0L. How different are the 1.7 and 1.8?
Posted by: euro911 Aug 19 2013, 06:12 PM
I believe they all have slightly different ID diameters and the 2.0L only have 3 stud holes instead of 4.
Posted by: r_towle Aug 19 2013, 06:23 PM
Get the right ones or they won't line up.
Get 2.0 liter spacers.
So, seeing as you don't have them, there is a phenomenon named hydro lock on carbed cars that can happen when you stop the car.
These motors actually get hotter right after you stop them, as a heat sync.
This can boil the fuel, overflow that fuel into the cylinder, then you cannot turn over the motor because its now filled with enough fluid to hydro lock the piston in place.
Spacers help prevent this so you isolate the carbs from the motor with some plastic....phenolic spacers are the normal thing we all use, cause they can be bought everywhere.
Rich
Posted by: last337 Aug 19 2013, 06:42 PM
Get the right ones or they won't line up.
Get 2.0 liter spacers.
So, seeing as you don't have them, there is a phenomenon named hydro lock on carbed cars that can happen when you stop the car.
These motors actually get hotter right after you stop them, as a heat sync.
This can boil the fuel, overflow that fuel into the cylinder, then you cannot turn over the motor because its now filled with enough fluid to hydro lock the piston in place.
Spacers help prevent this so you isolate the carbs from the motor with some plastic....phenolic spacers are the normal thing we all use, cause they can be bought everywhere.
Rich
I have never had a problem with the motor locking up to that point where it wont turn over again but then again I dont do much stop and go driving. If I do stop it is usually for a beer and a burger
Anyways, trying to understand a bit more...I know that dual carbs are preferred to singles because of the long runners and the fuel turning back to liquid in the runners. What other effects does the heat radiating to the intake and the carbs have on the engine performance?
Posted by: r_towle Aug 19 2013, 06:45 PM
CALL gprparts or pelicanparts.
You want the following, in my opinion.
Engine is 2.0 liter type 4 motor.
Two phenolic spacers
Four gaskets, head to intake manifold.
Two sets (could be four pieces) of weber manifold gaskets.
If you call, John at GPR or the team at pelican will help you fast and simple.
Rich
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